Add seescores diagnostic command, verify zero SEE-value drift

Board-representation migration section 4 item 4: seescores <filename>
(command.c, registered alongside script/sd) reads setboard lines from
an EPD file (same convention tests/ecm*.ep_ already use), generates
legal moves per position, and prints (FEN, SAN move, SEE value) for
every capture -- meant to be run once per GetAttacksBB toggle state
and diffed, closing a gap TestGetAttacks's attacker-list comparison
can't: whether _GetAttacksBB's attacker lists, though set-identical to
asm GetAttacks, still produce identical SEE() output once fed through
_MinLegalPiece's exchange simulation.

Run against all three curated suites (747 captures total: 51 + 351 +
345), same-commit asm-vs-GETATTACKS_BITBOARD=1 A/B build (same pair
used for the earlier sd10 comparison) -- output byte-identical, zero
diff, on all three. Confirms _GetAttacksBB is correct all the way
through to the final SEE() score every move-ordering decision actually
uses, not just at the raw attacker-list level.

precommit_check.sh clean. Default (no flag) release binary restored
after testing.

Only match_play.py remains unmet before full retirement of the old
mailbox GetAttacks implementation (section 7) -- deliberately deferred,
not run this pass.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Jntky4yGUTyQVaGCXms4F2

1 files changed, 19 insertions, 7 deletions

diff --git a/src/board_representation/MIGRATION.md b/src/board_representation/MIGRATION.md
index 313c74d..c6673ce 100644
--- a/src/board_representation/MIGRATION.md
+++ b/src/board_representation/MIGRATION.md
@@ -15,12 +15,13 @@ inline as a note rather than deleted, so a future session designing
 the separate migration doesn't have to rediscover it from git history.
 
 **Status: sections 1-3 (`bbPieces`/`bbPawns`-backed
-`_WhoAttacksSquareBB`/`_GetAttacksBB`), section 4 items 1-3 and 5, and
-section 6 (the `GETATTACKS_BITBOARD` toggle) all implemented, verified,
-and committed -- including a whole-engine `sd10` check across all three
-curated suites showing zero solve-count regression and +8.38%
-aggregate NPS. Only `match_play.py` (section 4 item 6 / section 7)
-remains unmet before full retirement of the old mailbox
+`_WhoAttacksSquareBB`/`_GetAttacksBB`), all of section 4, and section 6
+(the `GETATTACKS_BITBOARD` toggle) implemented, verified, and
+committed -- including a whole-engine `sd10` check across all three
+curated suites (zero solve-count regression, +8.38% aggregate NPS) and
+a `seescores` SEE-value diff across all 747 captures in those suites
+(byte-identical, zero diff). Only `match_play.py` (section 4 item 6 /
+section 7) remains unmet before full retirement of the old mailbox
 implementation, deliberately deferred for now. Section 5's whole-engine
 item and section 7's remaining items are otherwise done; section 8 not
 started.** See the per-section status notes below for specifics.
@@ -461,7 +462,18 @@ sequence.
    ECM/random positions, run once per `GetAttacksBB` toggle state,
    diffed. Catches any behavioral drift `TestGetAttacks`'s raw-list
    comparison might miss once results feed into `_MinLegalPiece`'s
-   exchange simulation. Not started.
+   exchange simulation. **DONE.** `seescores <filename>` (`command.c`,
+   registered alongside `script`/`sd`) reads `setboard` lines from an
+   EPD file (the same convention `tests/ecm*.ep_` already use),
+   generates legal moves per position, and prints `(FEN, SAN move, SEE
+   value)` for every capture. Run against all three curated suites (747
+   captures total: 51 + 351 + 345), once per binary from section 4 item
+   5's same-commit asm-vs-`GETATTACKS_BITBOARD=1` A/B build -- output
+   **byte-identical, zero diff**, on all three. Confirms `_GetAttacksBB`
+   is correct not just at the attacker-list level (`TestGetAttacks`)
+   but all the way through `SEE()`/`_MinLegalPiece`'s exchange
+   simulation to the final score every move-ordering decision actually
+   uses.
 5. **Full-suite behavioral check is mandatory here, not optional** --
    this is the one place this migration is *riskier* than the Eval
    constant work: `GetAttacks` feeds move ordering and pruning decisions